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When a TELNET session is initialised using PuTTY, I see that PuTTY is sending the following characters to the server at the beginning of the connection:

..... .....'.........

I was able to capture this using WireShark. The hex characters are as follows:

ff fb 1f ff fb 20 ff fb 18 ff fb 27 ff fd 01 ff fb 03 ff fd 03

Can you please help me understand why PuTTY sends these characters? I assumed it is something with the connection, but then, these characters are found in the DATA category of the WireShark capture.

Here is a video: https://www.youtube.com/watch?v=WGZru4KPmsM

  • Those look like standard telnet option negotiating sequences. You should probably spend more time to read about [telnet](https://en.wikipedia.org/wiki/Telnet) and the protocol specifications. – Some programmer dude Oct 29 '19 at 09:53
  • If these are standard telnet negotiating sequences, why does it not appear when telnet is initialised using other tools like zoc terminal, etc.? Why does this happen only with PuTTY? –  Oct 29 '19 at 09:59
  • Perhaps there's settings in the other client to not start with sending these option negotiating sequences? Or perhaps PuTTY is more telnet-compliant than the other clients? There are unfortunately many so-called "telnet clients" which only handles sending plain text and just don't care about the rich telnet protocol. – Some programmer dude Oct 29 '19 at 10:04
  • Please move your question to [su] (delete here, re-post there). It's [off-topic here](//stackoverflow.com/help/on-topic). – Martin Prikryl Oct 31 '19 at 08:56

1 Answers1

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Thanks to Some programmer dude and Elmi.

These extra chunk of characters are the negotiation sequences from PuTTY (client) to the server. Negotiations allow the client to have an enriched experience. A list of negotiation sequences in telnet protocol and their explanation is given here

If you are using PuTTY and do not need these sequences, go to Connection > Telnet and set the Telnet negotiation mode to Passive

Here is a link to Elmi's post